The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

Flash flooding hits Sydney streets

Heavy rainfall across NSW has led to flash-flooding, with parts of Sydney worst hit.

Waterlogged roads caused backed-up traffic in the harbour city while those on foot fared even worse in Tuesday's torrential rain.

The Bureau of Meteorology issued a severe thunderstorm warning just before 4pm for most of the northeastern quarter of NSW, with heavy rainfall, large hailstones and strong winds expected over the coming hours.